1. Field of the Invention
The present invention relates to a resin composition for fiber reinforced plastic. More particularly, it relates to a resin composition suitable for fiber reinforced plastic materials wherein fibers of high elasticity are employed.
2. Discussion of Background
It is well known to impregnate an epoxy resin or an unsaturated polyester resin to a reinforcing material such as carbon fibers or glass fibers, followed by curing to form molded products having various shapes and thicknesses. This method is now being used for the production of cylindrical molded products or shafts for sporting goods or primary or secondary structural materials for aircrafts, or for the production of various materials. The reinforcing material having a resin impregnated and serving as a matrix, is called prepreg and may be in the form of strands, sheets stretched in one direction or fabrics. To obtain a molded product having a desired shape, it is known to use a filament winding method which comprises winding prepreg strands, or a lay-up method which comprises laminating prepreg sheets.
To laminate prepreg sheets, it is important that the prepreg has a proper adhesiveness (tackiness) so that prepreg sheets adhere to one another at the time of laying up, and a flexibility (draping properties) so that laid up prepreg layers accurately reflect the shape such as a curved surface or cylinder. Under these circumstances, epoxy resin compositions having suitable tackiness and draping properties were proposed in Japanese Examined Patent Publications No. 5925/1983, No. 17535/1983 and No. 40975/1983 and Japanese Unexamined Patent Publications No. 43615/1986 and No. 127317/1987.
However, such conventional resin compositions had drawbacks that depending upon the shape or various properties such as mechanical and physical properties of the reinforcing material to be used, the operation efficiency depending upon the tackiness and draping properties substantially decreases, and consequently the operation tends to be cumbersome, or it is difficult to obtain a molded product having satisfactory properties.
Namely, such an operation prior to the molding depends heavily on the tackiness of the resin composition constituting the prepreg and on the draping properties of the prepreg inclusive of the reinforcing material. The draping properties of the prepreg varies not only by the influence of the resin composition but also by the characteristics of the reinforcing material. To minimize such an influence by the characteristics of the reinforcing material, it is considered to be advisable to employ a resin composition which enriches the draping properties of the prepreg.
Under such circumstances, the present inventors have previously found that by a combination of resins having specific physical properties, it is possible to obtain a prepreg having excellent draping properties (Japanese Unexamined Patent Publication No. 308026/1988), and further found a resin composition for improving the strength in the direction of 90.degree. C. when a on directional prepreg is prepared (Japanese Patent Application No. 40517/1988). They have further found that by blending a phenol novolak type epoxy resin to such as resin composition, a molded product having no internal voids after the thermosetting molding can be obtained while adequately maintaining the shape-maintaining strength of the prepreg sheets and excellent draping properties (Japanese Patent Application No. 170228/1988).
Such a resin composition does not create any particular problem when applied to fiber reinforced plastic materials wherein reinforcing fibers of usual physical properties are employed. However, in a case where the reinforcing fibers have a high modulus of elasticity, the tackiness tends to be slightly poor, and it frequently happens that the shape after the shape-forming can not be maintained.
Further, the fluidity at the time of thermosetting is substantial, and it may happen that when the curing speed is slow, the shape prescribed prior to the heating will be deformed, or a substantial amount of the resin component will flow out. As a result, the molded product tends to have void spaces or portions where the resin is inadequate, and it tends to be difficult to obtain a flawless molded product having high reliability.
Namely, the thermosetting resin containing a reinforcing material is required to have a proper fluidity as well as a proper curing speed for thermosetting.
Under these circumstances, the present inventors have conducted extensive researches and as a result, have found that by incorporating a phenol novolak type epoxy resin further to the previously proposed resin composition, it is possible to attain proper fluidity and proper curing speed while adequately maintaining the excellent draping properties and the shape-maintaining strength of the prepreg sheets, whereby it is possible to maintain the shape of the molded product after shaping and to obtain a molded product free from internal voids after thermosetting. The present invention has been accomplished on the basis of this discovery.
Namely, it is an object of the present invention to provide a resin composition for fiber reinforced plastic which is excellent in the operation efficiency while maintaining excellent draping properties and the shape-maintaining strength of prepreg sheets and which is capable of presenting a molded product having no voids in the interior of the molded product after thermosetting molding.
Such an object can be accomplished by a resin composition for fiber reinforced plastic comprising the following components A, B, C, D and E as essential components:
A: a bisphenol A type epoxy resin having an epoxy equivalent of at most 250 and being liquid at room temperature,
B: a bisphenol A type epoxy resin having an epoxy equivalent within a range of from 400 to 5,000 and softening point of from 60.degree. to 200.degree. C.,
C: a phenol novolak type epoxy resin,
D: a nitrile rubber, and
E: a curing agent.
Now, the present invention will be described in detail.
With respect to the bisphenol A type epoxy compound (component A) having an epoxy equivalent of at most 250 and being liquid at room temperature to be used in the present invention, there is no particular restriction so long as it has an epoxy equivalent of at most 250, preferably from 180 to 200 and it is liquid at room temperature. Specifically, the following compounds may be mentioned:
"EPIKOTE" 816, 827, 828, manufactured by Yuka Shell Epoxy Company,
"Araldite" GY250, GY260, manufactured by Ciba Geigy Company,
"AER" 334, 330, 331, manufactured by Asahi Chemical Industry Co., Ltd.,
"Sumiepoxy" ELA-115, ELA-127, ELA-128, manufactured by Sumitomo Chemical Co., Ltd.,
"EPICLON" 855, 840, 850, manufactured by Dai Nippon Ink Kagaku K.K.,
"EPOTOHTO" YD-115, YD-127, YD-128, manufactured by TOHTO KASEI CO., LTD.,
"EPOMIK" R130, R139, R140, manufactured by Mitsui Petrochemical Industries, Ltd.
With respect to the bisphenol A type epoxy resin (component B) having an epoxy equivalent of from 400 to 5,000 and a softening point of from 60.degree. to 200.degree. C., any such resin may be used long as it has an epoxy equivalent of from 400 to 5,000, preferably from 400 to 3,500 and a softening point of from 60 to 200, preferably from 60 to 160. Specifically, the following materials may be mentioned:
"EPIKOTE" 1001, 1002, 1004, 1004, 1007, 1009, 1010, manufactured by Yuka Shell Epoxy Company,
"Araldite" 6071, 7072, 6084, 6097, 6099, manufactured by Ciba Geigy Company,
"AER" 661, 662, 664, 667, 669, manufactured by Asahi Chemical Industry Co., Ltd.,
"Sumiepoxy" ESA-011, ESA-014, ESA-017, ESA-019, manufactured by Sumitomo Chemical Co., Ltd.,
"EPICLON" 1050, 4050, 7050, manufactured by Dai Nippon Ink Kagaku K.K.,
"EPOTOHTO" YD-011, YD-012, YD-014, YD-017, YD-019, manufactured by TOHTO KASEI CO., LTD.,
"EPOMIK" R301, R302, R304, R307, R309, manufactured by Mitsui Petrochemical Industries, Ltd.
This component B is preferably a mixture comprising component B1 which is a bisphenol A type epoxy compound having an epoxy equivalent of at most 1,000 and a softening point of at most 100.degree. C. and being solid at room temperature and component B2 which is a bisphenol A-epoxy compound having an epoxy equivalent of at least 110 and a softening point of at least 110.degree. C. and being solid at room temperature. Specific examples will be given for components B1 and B2, respectively.
With respect to the bisphenol A type epoxy compound (component B1) having an epoxy equivalent of at most 1,000 and a softening point of at most 100.degree. C. and being solid at room temperature, any such compound may be used so long as it has an epoxy equivalent of at most 1,000, preferably from 400 to 1,000, and a softening point of at most 100.degree. C., preferably from 60.degree. to 100.degree. C. Specifically, the following compounds may be mentioned:
"EPIKOTE" 1001, 1002, 1004, manufactured by Yuka Shell Epoxy Company,
"D. E. R." 667, 668, 669, manufactured by Dow Chemical Company,
"Araldite" 6071, 7072, manufactured by ciba Geigy Company,
"Suminepoxy" ESA-011, ESA-014, manufactured by sumitomo chemical Co., Ltd.,
"EPICLON" 1050, 4050, manufactured by Dai Nippon Ink Kagaku K.K.,
"EPOTOHTO" YD-011, YD-127, YD-012, YD-014, manufactured by TOHTO KASEI CO., LTD.,
"EPOMID" R301, R302, R304, manufactured by Mitsui Petrochemical Industries, Ltd.
With respect to the bisphenol A type epoxy compound (component B2) having an epoxy equivalent of at least 1,100 and a softening point of at least 110.degree. C. and being solid at room temperature, any such compound may be used so long as it has an epoxy equivalent of at least 1,100, preferably from 1,100 to 5,000, more preferably from 1,100 to 3,500, and a softening point of at lest 110.degree. C., preferably from 110.degree. to 200.degree. C., more preferably from 110.degree. to 160.degree. C. Specifically, the following compounds may be mentioned:
"EPIDOTE" 1007, 1009, 1010, manufactured by Yuka Shell Epoxy company,
"D. E. R." 6678, 668, 669, manufactured by Dow Chemical Company,
"Araldite" 6097, 6099, manufactured by Ciba Geigy Company,
"Sumiepoxy" ESA-017, ESA-019, manufactured by Sumitomo Chemical Co., Ltd.,
"EPICLON" 7075, 7055, 9050, manufactured by Dai Nippon Ink Kagaku K.K.,
"EPOTOHTO" YD-017, YD-119, manufactured by TOHTO KASEI CO., LTD.,
"EPOMIK" R307, R309, manufactured by Mitsui Petrochemical Industries, Ltd.
The phenol novolak type epoxy compound (component C) means a compound of the formula: ##STR1## wherein n is an integer.
As such a phenol novolak type epoxy resin (component C), the following compounds may specifically be mentioned:
"EPIKOTE" 152, 154, manufactured by Yuka Shell Epoxy Company,
"Araldite" EPN1138, EPN1139, manufactured by Ciba Geigy Company,
"D.E.N" 431, 438, 439, 485, manufactured by Dow Chemical Company,
"EPPN" 201, manufactured by Nippon Kayaku K.K.,
"EPICLON" N-730, N-738, N-740, manufactured by Dai Nippon Ink Kagaku K.K.
These compounds may be used alone or in combination as a mixture of two or more different types.
The nitrile rubber of component D is not particularly restricted, and it is usual to employ the one having an average molecular weight of at least 10,000. Specifically, a copolymer of butadiene and acrylonitrile may be employed. Further, it may be a copolymer having acrylic acid added to butadiene and acrylonitrile. It is usual to employ such copolymer having an average molecular weight of about 50,000. The acrylonitrile content is usually from 15 to 40% by weight.
The nitrile rubber of component D may be incorporated independently in the form of nitrile rubber to the epoxy resin composition of the present invention. However, it is preferred to preliminarily mixing and reacting it with the epoxy compound of component A so that it may be incorporated in the form of a nitrile rubber-modified epoxy compound thus obtained.
In the present invention, the above mentioned respective components are essential components, and their proportions are preferably such that relative to 100 parts by weight of component A, component B is from 5 to 40 parts by weight, component C is from 50 to 140 parts by weight and component D is from 1 to 8 parts by weight. More Preferably their proportions are such that relative to 100 parts by weight of component A, component B1 is from 5 to 40 parts by weight, component B2 is from 5 to 40 parts by weight, component C is from 50 to 140 parts by weight and component D is from 1 to 8 parts by weight. Further, it is important that the resin composition of the present invention has a viscosity at 40.degree. C. (.eta.40.degree. C.) of at least 10,000 poise, preferably from 10,000 to 40,000 poise, more preferably from 10,000 to 30,000 poise and a viscosity at 80.degree. C. (.eta.80.degree. C.) of at most 200 poise, preferably from 20 to 200 poise, more preferably from 50 to 150 poise.
If the viscosity (.eta.40.degree. C.) is less than 10,000 poise, the surface tends to be sticky although the operation efficiency may be improved. On the other hand, if it is too high, the operation efficiency tends to be poor, since the hardness tends to be too high.
If the viscosity (.eta.80.degree. C.) exceeds 200 poise, the moldability in heat molding tends to be poor. On the other hand, if the viscosity is too low, the flowability tends to be so excellent that the operation efficiency tends to be poor, such being undesirable.
Here, in the present invention, component A and component B primarily serve to adjust the viscosity of the resin composition. Particularly, in the present invention, the adhesive properties of the resin composition can be improved by the combined use of components B1 and B2. Component D serves primarily to impart excellent operation efficiency and is effective particularly for the improvement of the flexibility of the resin composition.
Component C serves to prevent formation of voids in the interior of the molded product. If components C and D are not incorporated, it tends to be difficult to impart good flexibility with a proper viscosity during the preparation of prepreg sheets or during the molding operation, and voids tend to form in the interior of the molded product, such being very inconvenient.
As far as the physical properties of the resin mixture can be maintained, other components such as an aliphatic epoxy resin, an o-cresol novolak type epoxy resin, a polyglycidyl amine, a bisphenol F type epoxy resin, a brominated bisphenol A type epoxy resin, 1,1,2,2-tetrabis(4-glycidoxyphenyl)ethane, a glycidyl ester type epoxy resin and a monofunctional epoxy compound, may further be incorporated, as the case requires.
The curing agent of component E may usually be any curing agent. It may be dicyandiamide, an acid anhydride, an aromatic diamine, dimercaptan or a phenol resin. Further, in order to impart storage stability and low temperature curability to the prepreg, it is effective to employ a combination of dicyandiamide and a curing accelerator. Even when dicyandiamide is used alone, no change is required in the operation prior to the molding, provided that the molding compositions such as the curing temperature may vary. The curing accelerator may be an imidazole derivative such as 2-ethyl-4-methylimidazole or 2-(2-cyanoethyl)-imidazole, or a urea derivative such as N-(3,4-dichlorophenyl)-N',N'-dimethylurea, N-(4-chlorophenyl)-N',N'-dimethylurea or N-(3-chlorophenyl)-N',N'-dimethylurea. In such a combination of curing agents i.e. a combination of dicyandiamide and a curing accelerator, it is preferred that dicyandiamide is incorporated in an amount of form 0.5 to 10 parts by weight, based on 100 parts by weight of the entire resin mixture, and the curing accelerator is incorporated in an amount of from 0.5 to 10 parts by weight.
The resin composition of the present invention is useful for fiber reinforced plastics. The reinforcing fibers may be glass fibers, carbon fibers, aramide fibers, alumina fibers or boron fibers. It is particularly preferred to employ carbon fibers having a high modulus of elasticity. Such fiber reinforced plastics may be prepared by usual methods such as a solution method or a heat melting method.